The present invention relates to a composite metal polybasic salt having a novel crystalline structure, a method of preparing the same and use thereof.
As synthetic composite metal hydroxides, there have heretofore been known a hydrotalcite-type synthetic mineral (e.g., Japanese Examined Patent Publication (Kokoku) No. 32198/1972) and a salt of lithium aluminum composite hydroxide (e.g., Japanese Examined Patent Publication (Kokoku) No. 2858/1995).
There has further been known a polybasic aluminum-magnesium salt. Japanese Examined Patent Publication (Kokoku) No. 38997/1974 teaches a method of producing a polybasic aluminum salt by reacting a polybasic aluminum sulfate with a magnesium hydroxide at a molar ratio of Al/Mg=1/2 to 4/3 in the presence of water. There has been further stated that the polybasic aluminum magnesium salt can be effectively used as an antacid.
Japanese Unexamined Patent Publication (Kokai) No. 204617/1985 teaches a method of preparing a magaldrate expressed by the formula Al5Mg10(OH)31(SO4)2.xH2O by reacting an active aluminum hydroxide with a stoichiometric amount of water-soluble sulfate-containing compound, active magnesium oxide and(or) magnesium hydroxide in the presence of water and, if necessary, drying the resulting magaldrate paste.
Japanese Unexamined Patent Publication (Kokai) No. 102085/1989 discloses a novel aluminum magnesium hydroxy compound represented by the formula AlxMgy(OH)35xe2x88x92zR2.nH2O [wherein R is a residue RC00- of monocarboxylic acid, and indexes x, y and z satisfy the following conditions 3xe2x89xa6x xe2x89xa69, 4xe2x89xa6yxe2x89xa613, 3xe2x89xa6zxe2x89xa65 and 3x+2y=35].
Japanese Unexamined Patent Publication (Kokai) No. 164432/1989 discloses an aluminum magnesium hydroxy compound having a layer structure represented by the general formula AlxMgy(OH)35xe2x88x92zR2.nH2O [wherein R is a residue RC00- of monocarboxylic acid, RC00- having 2 to 22 carbon atoms, and indexes x, y and z satisfy the following conditions 3xe2x89xa6xxe2x89xa69, 4xe2x89xa6yxe2x89xa613, 3xe2x89xa6zxe2x89xa65 and 3x+2y=35], and a gel composition containing an oleophilic organic compound which is in the liquid form at room temperature (20xc2x0 C.).
Japanese Examined Patent Publication (Kokoku) No. 59977/1989 discloses a crystalline basic aluminum magnesium carbonate represented by the formula Al2Mg6(OH)12(CO3)2.xH2O [wherein xxe2x89xa64].
Further, Japanese Examined Patent Publication (Kokoku) No. 52409/1991 discloses a method of producing a hydroxyaluminum magnesium sulfate by reacting a solid magnesium hydroxide and/or magnesium oxide with an aqueous solution of aluminum sulfate at an atomic ratio of magnesium:aluminum of from 1:1 to 3:1 until the pH of the reaction mixture becomes 4.0 to 8.0, removing the water-soluble component from the reaction mixture by a known method, followed, if necessary, by drying.
A conventional polybasic aluminum magnesium salt, e.g., a USP-referred standard magaldrate exhibits diffraction peaks at 2xcex8=10 to 12xc2x0, 2xcex8=22 to 24xc2x0, 2xcex8=33 to 35xc2x0, 2xcex8=45 to 47xc2x0 and 2xcex8=60 to 63xc2x0 in the X-ray diffraction (Cu-xcex1), whereas the polybasic aluminum magnesium salt of the present invention in which the anions are sulfuric ions exhibits diffraction peaks at 2xcex8=2 to 15xc2x0, 2xcex8=19.5 to 24xc2x0 and 2xcex8=33 to 50xc2x0 in the X-ray diffraction (Cu-xcex1), and a single peak at 2xcex8=60 to 64xc2x0. The present inventors have succeeded in synthesizing a novel composite metal polybasic salt that has an explicit crystal structure exhibiting a single X-ray diffraction (Cu-xcex1) peak at 2xcex8=33 to 50xc2x0, the crystal structure being different from those of hydrotalcites.
The inventors have further discovered that the composite metal polybasic salt can be effectively used as an additive for resins, as a heat insulator and as an anion-exchanger.
The object of the present invention is to provide a composite metal polybasic salt containing a trivalent metal and magnesium as metal components and having a novel crystal structure, and a method of preparing the same.
Another object of the present invention is to provide a composite metal polybasic salt which has anion-exchanging property, which by itself is useful as an anion-exchanger, capable of introducing anions suited for the use upon anion-exchange, and finds a wide range of applications, and a method of preparing the same.
According to the present invention, there is provided a composite metal polybasic salt having a chemical composition represented by the following general formula (1),
M3+pMgq(OH)y(A)z.nH2Oxe2x80x83xe2x80x83(1)
wherein M3+ is a trivalent metal, A is an inorganic or organic anion, and p, q, y and z are numbers satisfying the following formulas,
(i) 3p+2qxe2x88x92yxe2x88x92mz=0 (wherein m is a valency of anion A),
(ii) 0.3xe2x89xa6q/pxe2x89xa62.5,
(iii) 1.5xe2x89xa6y/(p+q)xe2x89xa63.0, and
(iv) 4.0xe2x89xa6(p+q)/zxe2x89xa620.0, and
n is a number of not larger than 7, exhibiting diffraction peaks at 2xcex8=2 to 15xc2x0, 2xcex8=19.5 to 24xc2x0and 2xcex8=33 to 50xc2x0, and a single peak at 2xcex8=60 to 64xc2x0 in the X-ray diffraction (Cu-xcex1), and having a degree of orientation (I0) represented by the following formula (2) of not smaller than 1.5,
I0=I10/I60xe2x80x83xe2x80x83(2)
wherein I10 is an X-ray diffraction peak intensity at 2xcex8=2 to 15xc2x0, and I60 is an X-ray diffraction peak intensity at 2xcex8=60 to 64xc2x0.
In the present invention, it is desired that an X-ray diffraction (Cu-xcex1) peak at 2xcex8=33 to 50xc2x0 is a single peak.
In the present invention, it is desired that the trivalent metal (M3+) in the above formula is aluminum. In this case, q/p can be not larger than 2.0.
In the present invention, further, it is desired that the anions (A) in the above formula are sulfuric acid ions. The sulfuric acid ions have anion-exchanging property, and can be exchanged with carbonic acid ions, organocarboxylic acid ions, phosphoric acid ions, silicic acid ions, perchloric acid ions, aluminic acid ions or sulfonic acid ions.
The composite metal polybasic salt of the present invention exhibits X-ray diffraction peaks at the above-mentioned Bragg angle. For example, the Alxe2x80x94Mgxe2x80x94SO4 composite metal polybasic salt which is a product of the invention, generally, has the following X-ray diffraction image:
In this case, the degree of orientation (I0) is from 2 to 20.
When photographed by using a scanning-type electron microscope, the composite metal polybasic salt of the present invention has a pleat-like thin-piece texture with a honeycomb-type or pumice-type internal structure.
Among the above X-ray diffraction peaks, a peak at 2xcex8=33 to 50xc2x0 is singular, and a laminate asymmetric index (Is) defined by the following formula (3),
Is=tan xcex82/tan xcex81xe2x80x83xe2x80x83(3)
wherein xcex81 is an angle subtended by a peak perpendicular in the X-ray diffraction peak of a predetermined spacing and a peak tangent on the narrow angle side, and xcex82 is an angle subtended by the peak perpendicular at the above peak and a peak tangent on the wide angle side, is not smaller than 1.5 at a peak of 2xcex8=33 to 50xc2x0.
According to the present invention, there is further provided a method of preparing a composite metal polybasic salt by reacting a water-soluble salt of a trivalent metal with an oxide, a hydroxide or a water-soluble salt of magnesium under the conditions of a pH of from 6.0 to 9.0 and a temperature of not lower than 50xc2x0 C. and, preferably, not lower than 80xc2x0 C. and, if necessary, executing the ion exchange in the presence of an acid or a soluble salt of acid.
According to the present invention, further, there is provided an additive for resins, a heat insulator and an anion-exchanger comprising the composite metal polybasic salt.
In the anion-exchanger, it is desired that the anions of the composite metal polybasic salt are sulfuric acid ions.